Optical fiber amplifiers are commonly used in communication systems. Examples of optical fiber amplifiers include Erbium Doped Fiber Amplifiers (“EDFA”) and other type of Rare Earth Doped Fiber Amplifiers. These optical fiber amplifiers are usually pumped by light emitter diodes (LEDs) or lasers. FIG. 1a and FIG. 1b each illustrate that an EDFA 100 is optically pumped by two polarized light sources, such as, two polarized lasers.
FIG. 1a illustrates a backward pumping scheme. With the backward pumping scheme, the optical signal to be amplified and the pumping light travel in opposite directions. A first pump light P1 received from pump laser one and a second pump light P2 received from pump laser two are combined by a Polarization Maintenance (“PM”) combiner 124. The output from PM combiner 124 is transmitted through an isolator 125 to a Wavelength Divisional Multiplex (“WDM”) coupler 126 as combined pumping light. The combined pumping light exits from WDM coupler 126 and enters EDFA 100. An input optical signal Si is optically coupled to EDFA 100 and travels a direction opposite to the traveling direction of the pumping light. Input optical signal Si is amplified in EDFA 100, passes through WDM coupler 126 and an isolator 127, and becomes output light So.
FIG. 1b illustrates a forward pumping scheme. With the forward pumping scheme, the optical signal to be amplified and the pumping light travel in the same direction. A first polarized light P1 received from pump laser one and a second polarized light P2 received from pump laser two are combined by a PM combiner 134. The output from PM combiner 134 is transmitted through an isolator 135 to a WDM coupler 136 as combined pumping light. The combined pumping light exits from WDM coupler 136 and enters EDFA 100. An input optical signal Si, after passing through an isolator 137 and a WDM coupler 136, enters EDFA 100 and travels in the same direction as the traveling direction of the pumping light. Input optical signal Si is amplified in EDFA 100, and becomes output light So.